Method of and apparatus for radiographic examination



1,622 149 March 22? 1927. A. ST. JOHN METHOD OF AND APPARATUS FOR RADIOGRAPHIC EXAMINATION Filed July 26 1923 Patented Mar. 22, 1927.

UNITED siATEs PATENT OFFICE. y

ANGEL ST. JOHN, OF BROOKLYN, NEW YORK, ASSIGNOR T UNION CARBIDE &l CARBON RESEARCH LABORATORIES, INC.,

A CORPORATION OF NEW YORK.

imrnon or` im APPARATUS ron aaiiioeanriiic EXAMINATION.

Application tiled .Tuly 26,

This invention is a method of radio raphic examination, and includes a novel g-ray tube adapted for use in the method.

X-ray tubes are usually of glass, and theA source of X-rays, the target or anticathode, is centrally arranged, and as -far from the glass wall of the tube as the size of the tube will permit. This gives a symmetrical arrangement and protects the glass from the heat generated at the anticathode.

With the central arrangement of anticathode, a material to be examined cannot be brought close to the source of X-rays, and as a result the rays striking` any small portion of the material travel inlines which are nearly parallel, as will appear from Fig. 1 of the accompanying drawing, in which Fig. 1 illustrates the examination of a V- weld with the usual type of X-ray tube, and

2o Fig. 2 shows an X-ray tube embodying my invention, and illustrates my novel method.

'The V-weld shown in section inFig. 1 has two scarfs disposed at an angle of sa 75. The extreme divergence of X-rays fallin on the Weld is the angle 0, hence much less t an the angle between the two scarfs. Imperfections are more apt to occur in the scarfs than elsewhere in the weld, and in imperfect welds there is often a fissure along one or both scarfs where the added metal is not in contact or in welded relation with the base metal, though the weld may be perfect at both surfaces of the plate. Therefore no radiographic examination of the weld which does not critically test the. scarfs can prove the soundness of the Weld. f

It will be understood, of course, that the width of any fissures present is almost always very small inv comparison with the thickness of the plate. As a result, the mcrease in transparency to X-rays brought about by the presence of a fissure will be negligible when the rays pass transversely of the fissure, and if the examination is limited to a test in which the radiation travels only in this direction, theissure will escape detection. A complete radiographic examination of a weld with equipment now available involves placing-the weld in several different positions with respect to the tube and locating any regions of abnormally high transparency by the use of a fluorescent screen, photographic (plate or other instrumentality visibly affecte by X-rays. It is only when u a fissure is turned substantially parallel to ibas. serial nu. 653,997.

the direction of propagation of the rays that its presence will be readily detected.

In Fig. 2 I have shown an arrangement, including an X-ray tube of novel design, whereby it becomes unnecessary to bring a lissure 1nto aparticular plane in order to detect it. In fact, all the fissures which can occur in a weld, whether parallel' or not, canl 14 of tungsten or other metal. The interior of the tube is of course evacuated, and the anticathode 14 should be very thin so as to out down absorption, since the X-rays to be used are emitted from the inner sur- `tbe anticathode from atmospheric pressure,

from oxidation, and from accidental me chanical impacts. The anticathode and its cover may be assembled with a threaded ring 16 and one or more gaskets 17 to in= sure a gas-tight seal. The anticathode may beprovided with .a in-hole (not shown) to permit the space etween 14 and 15 to be evacuated, thereby better protecting the anticathode from oxidation'and from atmospheric pressure.

A passage 18 in collar 13 permits watercooling of the anticathode assembly. The member 15 will remain sufficiently cool to prevent its destruction.

The cathode filament 19 and focusing tube 2O are of well-known construction and so arranged as to give a broad focal spot, forl example one-'half inch in diameter, on the anticathode 14.

The anticathode is electrically connected with the metal tube 10, and the latter may be provided with a flange 21 for connecting weld in the position shownX-rays will pas` along both scarfs and also through the weld in man other directions. Any imperfection whlch seriously diminishes the strength of the weld will have a relatively large dimansion alon some plane not parallel with the surface o the plate, and such an imperfection will be readil apparent from the abnormal intensity o the radiation transmitted through it along this plane. It will be seen that no exact orientation of the weld with respect to the tube is required. In Fig. 2 the weld could be rotated throu h a conslderable an le in the lane of t e paper and the res ts would still be equally good. f

Upon merely bringin the weld before and close to the anticatho e, a complete examination can be effected with a single exposure.

Having now described my invention, claim:

1. Method of detecting-defects in objects a0 wherein the tendency toward defects is lo calized along diver 'ng lines, which comprises simultaneous propagating X-rays through the object a ong a plurality of said diverIing1 lines. v

2. et od of radiographically examinin welds havin strong! divergent scar which comprises simu taneousl propagating X-rays through the'weld 1n drectlons parallel to a plurality of scarfs. t In testimony whereof, I aix my signaure.

ANGEL sr. Jomr. 

